GCS Game World and Valve announce that S.T.A.L.K.E.R.: Clear Sky will be available for digital download worldwide exclusively on Steam. The official prequel to the Survival FPS game S.T.A.L.K.E.R.: Shadow of Chernobyl is currently slated for simultaneous release on Steam and at retail outlets later this year. S.T.A.L.K.E.R.: Clear Sky brings the players one year prior to the events of the original S.T.A.L.K.E.R. game in 2011. A group of stalkers has, for the first time, reached the very heart of the Zone-Chernobyl Nuclear Power Plant-and brings about a cataclysm on the brink of a catastrophe. Through a rich narrative and gripping combat action, players uncover new challenges and insights in the Exclusion Zone. A new version of the game engine, X-Ray 1.5, powers superior graphical details and realistic and non-scripted combat AI. More information and a collection of new images may be found here.